Make WindowRenderer::resume async (w/callback) for wasm-friendly wgpu init

#59 in DioxusLabs/anyrender — merged 2026-05-10

Adds an async resume_async method to WindowRenderer so GPU backends can drive wgpu's fundamentally-async surface initialization without pollster::block_on deadlocking the JS event loop on wasm32-unknown-unknown. The default body forwards to sync resume (non-breaking for downstream impls); anyrender_vello and anyrender_vello_hybrid override it with a real async body and now panic! from sync resume on wasm32 instead of silently deadlocking.